1. Field of the Invention
The present invention relates to a color measuring apparatus for continuously measuring a color value of a sample, which is used for monitoring, for example, a change of a baked color with time due to baking or change of combination color through mixing of dyes.
2. Description of the Prior Art
Color measuring apparatuses are known which project ambient light onto surface of a sample and receive and analyze reflected light from the sample so as to discriminate color of the sample.
Meanwhile, in the case where a change of a baked color due to baking or a change of a combination color through mixing of dyes is continuously monitored by the known color measuring apparatuses such that the baking or the mixing of the dyes is stopped at the time when the measured color value of the sample has most approximated to a target color value, it can be considered that by calculating a distance between the measured color value and the target color value in two or three dimensions, a point of inflection at which the distance is shifted from a decreasing phase to an increasing phase, is detected so as to be regarded as representing a color value most approximate to the target color value. However, the measured color value does not necessarily approach to the target color value monotonously. Thus, if it is decided that an initial point of inflection appearing after the start of measurement represents the color value most approximate to the target color value, such a phenomenon as insufficient baking, etc. may take place. Hence, it is desirable to seek a point of inflection which can be regarded as really representing a color value most approximate to the target color value. Nonetheless, if such point of inflection is sought by neglecting so many points of inflection, such a state may also be created that the measured color value steadily departs from the target color value, thereby resulting in excessive baking, etc. In this case, it is understood that the baking, etc. should have been stopped at the previous point of inflection. Thus, in the case where the measured color value does not necessarily coincide with the target color value completely and the color value of the sample cannot be reinstated to the color value most approximate to the target color value after passing through the color value most approximate to the target color value, it is necessary to accurately detect the point of inflection which can be regarded as representing the color value most approximate to the target color value. However, the known color measuring apparatuses could not meet such requirements.
Furthermore, when a change of color of a sample is automatically measured repeatedly as in the case where change of baked color due to baking or change of combination color through mixing of dyes is monitored, a measuring time interval should be shortened, for the purpose of frequently collecting measured data, in a region in which the color of the sample is approximate to the target color value. However, in the known color measuring apparatuses, it is not so arranged that a time interval of automatic measurement is changed according to a color value of the sample. Thus, the known color measuring apparatuses have such a drawback that even in a region in which the color of the sample deviates far away from the target color value, automatic measurement is performed at a short time interval with the result that measured data is outputted frequently.